Institute for Work & Health, 20018
A Case-Control Study of Biomechanical and Psychosocial
Risk Factors for Occupational Low-Back Pain
Michael S. Kerr, PhDInstitute for Work & HealthToronto, Ontario, CANADA
PREMUS 2001, Amsterdam
Kerr et al. (2001) Am J Pub Health 91:1069-1075
Institute for Work & Health, 20018
Study Collaborators
Institute for Work & Health:Kerr MS, Frank JW, Shannon HS, Bombardier C
University of Waterloo:Norman RW, Wells RW, Neumann PGeneral Motors: Mr. Elmer BeddomeCAW: Mr. John Graham
The Ontario Universities Back Pain Study (OUBPS) Group
Andrews D, Beaton DE, Dobbyn M, Edmonstone E, Ferrier S, Hogg-Johnson S, Ingelman P, Mondlock M, Peloso P, Smith J, Stanfield SA, Tarasuk V, Woo H
Institute for Work & Health, 20018
Why a case-control study?
• Uncertainty about role of physical demands necessitated concentration of effort on developing valid workplace measures
• Cohort model required multiple measures at multiple times to assess valid exposure
Does a prospective cohort study with limited (e.g. once only) exposure assessment really provide more rigorous evidence than a case-control study with more detailed assessments?
Institute for Work & Health, 20018
Research Question
After controlling for individual characteristics, what are the main work-related biomechanical and psychosocial risk factors for reported low-back pain?
Institute for Work & Health, 20018
STUDY SETTING
GM-Oshawa autoplex65 km east of TorontoTotal hourly-paid work force – approx. 12,0003 Divisions: Car Assembly (7,000)
Truck Assembly (3,000)Fabrications N/A
Nursing stations – handle ALL WCB reports as well as most other health problems occurring at work-site Truck = 1 station; Car = 4 stations
Institute for Work & Health, 20018
The GM Study of Low-back Pain
baseline questionnaire and
physical exam
10,000 car and truckplant workers (hourly-paid)
random
selection(job-matched)
accrued viaworkplace health
stations
conducted
at home
physical demands assessment
CASES
workers without
LBP
STUDY POPULATION
workers with LBP
CONTROLS
Incidence density sampling
at work doingusual job
video, EMG, checklists, posture
(n=137)
(n=179)(n2=65)
Institute for Work & Health, 20018
SUBJECT ENROLMENT
(Voluntary)
179
137
65
Random controls
Cases
A total of 381 subjects enrolled
in the study
Job-matched controls(used for proxy data)
Institute for Work & Health, 20018
CASE Definition
• Full-time, hourly-paid worker with “sprain-strain” LBP (reported to nursing stations)
• No lost-time or WCB claim requirement
• No previous worksite LBP report (90 days)
Institute for Work & Health, 20018
SF-36, Health-related quality of life
PhysicalFunction
Role –Physical
BodilyPain
SocialFunction
Vitality Role –Emotional
MentalHealth
GeneralHealth
Were cases and controls comparable except for LBP?
sd f
rom
mal
e re
fere
nce
popu
latio
n
Ref: Garrat et al. (1993) BMJ 306:1440-4
Institute for Work & Health, 20018
INDIVIDUAL Characteristics
Age, height, weight, body mass index, sex education, marital status, preschool children, main wage earner, non-occupational physical activity, smoking, alcohol consumption
STUDY VARIABLES - 1
Institute for Work & Health, 20018
BIOMECHANICAL Factors
• Peak Forces:compression; shear; hand force
• Cumulative Forces:average and integrated compression;
• Low-level (static) Forces:compression
• Posture and Movement:peak flexion; time non-neutral; trunk kinematics
(reduced a priori to about 20 key variables, NO EMG)
STUDY VARIABLES - 2
Institute for Work & Health, 20018
STUDY VARIABLES - 3
PSYCHOPHYSICAL Factors
self-rated physical exertion measures
distinct from "objective" measurements of physical demands analyses, but may also have additional role to play over and above the measured demands
e.g. tolerance levels, "job stress", etc.
Institute for Work & Health, 20018
• Karasek-Theorell Job Content Instrument
• "psychological demand", decision latitude, supervisor support, coworker support, workplace social environment, job self-identity
• - job dissatisfaction, mastery, empowerment, status inconsistency ("over-education")
STUDY VARIABLES - 4
PSYCHOSOCIAL Factors
Institute for Work & Health, 20018
Summary of Key Risk Factors
0
1
2
3
Peak Shear
Peak hand force
Disc Compression
Series 4
Self-rated demands
Series 6
Poor Social Environment
Over-education
High Co-worker support
High Job Satisfaction
Low Job Control
PsychosocialBiomechanical
Odds Ratio
(Cumulative)
(Exertion)
(* p=0.07)
(p<0.05)
(after adjusting for individual characteristics)
Institute for Work & Health, 20018
Study Strengths
• Directly measured physical demands data combined with (basic) physical exam and interview-assisted psychosocial data for individual subjects
• Comprehensive workplace job demands assessments (generalizable – i.e. not specific to automobile manufacturing)
• Well defined study base for subject selection
Institute for Work & Health, 20018
Study Weaknesses
• Modest participation rate (approx 60%)• Relied on workplace reporting
mechanism to identify cases• Self-report only for psychosocial factors• Case-control design
But … does a prospective cohort study with limited once only exposure assessment really provide more rigorous evidence than a case-control study with more detailed assessments?
Institute for Work & Health, 20018
How did we control for Bias?
• Directly measured physical demands data rather than self-report
• Job-matched controls used to examine potential recall bias (none observed)
• Used newly incident cases rather than prevalent cases
• Compared cases with non-participating compensation claimants (no differences)
• A priori reduction in variables eligible for regression modeling (multi-methods)
Institute for Work & Health, 20018
Possible Biological Mechanisms
HORMONESe.g. cortisol
MUSCLETENSION
PSYCHOSOCIAL LOAD
INDIRECT EFFECTS
PSYCHOSOCIAL LOADe.g. job control
BIOMECHANICAL LOAD
e.g. cumulativecompression
DIRECT EFFECTS
BIOMECHANICAL LOAD
TOLERANCEREDUCED
TOLERANCEEXCEEDED
TISSUE RESPONSE
Institute for Work & Health, 20018
Main Conclusions
• Consistency and strength indicates biomechanical load increases LBP risk
• Psychosocial factors also shown to be associated with reporting LBP
• Job dissatisfaction not a risk factor for reporting LBP in this setting
• Psychosocial instruments (especially Karasek’s demands scale) may require further refinement for MSK studies
Institute for Work & Health, 20018
For additional information please contact:
Mickey KerrThe Institute for Work & Health
481 University Ave., Suite 800Toronto, ON M5G 2E9Phone: (416) 927-2027
Fax: (416)-927-4167Website: http://www.iwh.on.ca
E-mail: [email protected]
The Institute for Work & Health operates with the support of the Ontario Workplace Safety & Insurance Board
Kerr et al. (2001) Am J Pub Health 91:1069-1075
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